1. Field of the Invention
Exemplary embodiments of the present invention relate to a motor driving apparatus, and more particularly, to a motor driving apparatus which is capable of reliably monitoring an operating state of a motor, that is, a motor driving apparatus which is capable of observing a monitoring circuit for monitoring an operating state of a motor in real time, and thus determining whether the monitoring circuit normally operates.
2. Description of the Related Art
Currently, an apparatus for electronically controlling a steering apparatus of a vehicle has been generalized, and has so far progressed a lot. The electronic steering apparatus having no mechanical link between a steering apparatus and wheels may convert information on torque, speed, and direction of the steering apparatus into an electrical signal, and directly controls the wheels based on the electrical signal. Since there is no mechanical link between the steering apparatus and the wheels, a function for controlling the steering apparatus may be freely added. That is, a function for optimizing a driver's feel, a self-adjustment function, or a variable gear ratio may be easily and economically accomplished.
The electronic control for a steering apparatus may be performed through an electronic control unit (ECU). The electronic control method using such a processor is required to secure reliability, in order to minimize a malfunction. Furthermore, since the process for controlling wheels through the ECU is performed by a brushless AC (BLAC) motor, it is more important to secure reliability, in order to minimize a malfunction of the BLAC motor. Since a malfunction of the BLAC motor is a large risk factor in operation stability, research has been conducted on a method for preventing a malfunction.
Conventionally, the electronic steering apparatus includes a BLAC motor and a fail-safe DC motor. When the BLAC motor fails, the DC motor is operated according to the control of the ECU, and thus guarantees the performance of the electronic steering apparatus.
In such a system, the BLAC motor requires instantaneous torque control, and the position information of a rotor is needed for the instantaneous torque control. The position information of the rotor may be detected through a hall sensor which is a position sensor mounted in the BLAC motor. However, since the hall sensor is expensive, research has been conducted on a method for detecting the position information of the rotor without a hall sensor.
In the conventional method, since the initial angle of the rotor cannot be acquired and the reliability of a circuit to monitor the position information of the rotor cannot be sufficiently secured, the BLAC motor is likely to instantly malfunction. In order to solve such a problem during initialization, research has been conducted on a method using both of the DC motor and the BLAC motor.
Korean Patent Laid-open Publication No. 10-2006-0007557 has disclosed a method for calculating a reference angle in an electronic steering system which includes a BLAC motor and a fail-safe DC motor. The method calculates a reference angle of a motor in consideration of fail and safe, when an electronic steering apparatus of a vehicle is operated. This method is characterized in that the electronic steering apparatus is initially driven through the motor and the BLAC motor is then driven. At this time, the ECU detects a counter electromotive force caused by the BLAC motor, and calculates the reference angle.
In such a structure, however, when a monitoring circuit for detecting a counter electromotive force has no reliability, a malfunction may occur in the operation of the BLAC motor. Thus, according to a conventional method, two monitoring circuits having the same configuration are used to verify the reliability of the monitoring circuits. In this case, the detection results of the monitoring circuits are compared to determine whether a failure occurred.
FIG. 6 is a configuration diagram of a conventional motor driving apparatus.
As illustrated in FIG. 6, the conventional motor driving apparatus includes an actuator 100, a control unit 200, a monitoring unit 300, and a driving signal generation unit 400. The actuator 100 converts electric energy into rotary motion. The control unit 200 analyzes information of a monitoring circuit so as to control the actuator 100. The monitoring unit 300 is positioned between the actuator 100 and the control unit 200 so as to monitor the state of the actuator 100. The driving signal generation unit 400 is positioned between the actuator 100 and the control unit 200 so as to generate a driving signal for driving the actuator 100 according to the control of the control unit 200.
The actuator 100 for converting electric energy into rotary motion uses a BLAC motor. The BLAC motor is used when an electronic steering apparatus transmits motion of a steering apparatus to wheels. The BLAC motor is characterized in that it may be driven without a brush.
That is, the BLAC motor has a structure in which a coil for receiving electricity is not attached to a rotor but attached to a stator, and a magnet is attached to the rotor. A conventional motor can change the direction of a current, supplied to a coil according to rotation, through a brush. However, the BLAC motor is required to detect the rotation angle of the rotor, in order to change the direction of a current based on rotation.
The rotation angle of the BLAC motor may be detected through a hall sensor at each of phases U, V, and W of the BLAC motor. The hall sensor refers to a sensor capable of detecting a current which is generated in proportion to the change in magnetic field of a conductor through which a current is passed. The current change of the hall sensor may indicate the change in magnetic field of the BLAC motor, and the rotation angle of the rotor may be calculated through the change in magnetic field. However, when the hall sensor is attached, the internal structure of the BLAC motor may become complex. Thus, there has been used a method for detecting the rotation angle of a rotor by detecting the change in current of a coil without a hall sensor.
That is, in order to acquire the rotation angle of the rotor inside the BLAC motor, the current of the coil of the stator inside the BLAC motor may be detected to estimate the rotation angle. The current outputted from the coil may be used to detect a counter electromotive force generated through the BLAC motor. The counter electromotor force may be used to acquire the rotation angle of the rotor.
The control unit 200 serves to analyze the information of the monitoring unit 300 so as to control the actuator 100. The control unit 200 may control the actuator 100 by analyzing a counter electromotive force of the actuator 100. The rotation angle of the actuator 100 may be acquired from the counter electromotive force (voltage) of the actuator 100, and a rotation angle to be controlled later may be set on the basis of the torque, direction and speed of the steering apparatus.
Furthermore, the control unit 200 may determine whether the monitoring unit 300 normally operates. At this time, two or more monitoring units 300 may be additionally provided, and outputs of the respective monitoring units 300 may be compared to determine whether a failure occurred or not. The control unit 200 may use a microprocessor and a digital signal processor (DSP) to calculate the reliability.
The monitoring unit 300 is positioned between the actuator 100 and the control unit 200 so as to monitor the state of the actuator 100, and serves to measure a current of each phase extracted from the actuator 100.
At this time, a shunt resistor is used to measure the current. The shunt resistor is connected in series to the coil of the BLAC motor. Since a resistor has a characteristic of consuming a current flowing therein into heat, a shut resistor having a small resistance value may be selectively used. However, as the resistance value decreases, an error may occur in a measured current due to the influence of surrounding noise. Thus, the shunt resistor may be selected in consideration of the resistance value. The current measured through the shunt resistor is converted into a voltage and then supplied to the control unit 200.
The driving signal generation unit 400 is positioned between the actuator 100 and the control unit 200, and generates a driving signal for operating the actuator 100 according to the control of the control unit 200. The driving signal generation unit 300 is controlled through positive control and negative control.
The actuator 100 controls a load of the motor, which is divided into three phases including phase U, phase V, and phase W. The actuator 100 is driven in a different manner depending on the internal configuration thereof. In general, the actuator 100 independently controls current supply for each phase, in order to perform positive control and negative control for each phase. The current control may be performed through an FET, and a high-power switching circuit using an FET may be provided. The switching circuit is independently used to supply a positive voltage and a negative voltage to each of the phase U, the phase V, and the phase W. That is, the switching circuit may include a positive voltage supply switching circuit and a negative voltage supply switching circuit for the phase U, a positive voltage supply switching circuit and a negative voltage supply switching circuit for the phase V, and a positive voltage supply switching circuit and a negative voltage supply switching circuit for the phase W.
In such a method, however, the size of the monitoring circuit and the number of parts in the monitor circuit may be increased, while power consumption is increased. Thus, there is a demand for a structure capable of determining whether a failure occurred, using one monitoring circuit.
[Patent Document] Korean Patent Laid-open Publication No. 10-2006-0007557